This invention relates to a method of making a semiconductor device, and more particularly to an improved impurity diffusion method.
Several diffusion methods are known. Among these methods, solid-to-solid diffusion methods are believed to have many advantages.
One method is to use an impurity doped oxide as a diffusion source. For details, see J. Electrochem. Soc. SOLID-STATE SCIENCE AND TECHNOLOGY October 1972 Vol. 119, No. 10, pp. 1389 - 1394.
Another method is to use a single doped poly-silicon layer as a diffusion source. For details, see Proceedings of the 4th Conference on Solid State Devices, Tokyo, 1972 Supplement to the Journal of the Japan Society of Applied Physics, Vol. 42, 1973, pp. 101 - 109.
In the former method surface damage is often observed after diffusion, and in the latter method the flatness of the diffused to region is also impaired, thus limiting the use of the method to a narrow field.